Find a formula for the general term (not the partial sum) of the infinite series. Assume the infinite series begins at n = 1. 13, 19, 127, 181, ...

a) aₙ = 6n + 7
b) aₙ = 6n - 7
c) aₙ = 6n² - 7
d) aₙ = 6n² + 7